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Active ingredient

Sildenafil

Sildenafil is the active ingredient in a group of medicines used to treat erectile dysfunction in adult men. It belongs to a class of drugs called phosphodiesterase type 5 (PDE5) inhibitors. It is the generic equivalent of the originally branded medicine Viagra. It is used to help men who have difficulty achieving or maintaining an erection sufficient for sexual activity.

Reviewed by the Kam4eu Pharmacy Team on 13 August 2026 · Next review August 2027

Sildenafil medicines we deliver

Browse the full Erectile Dysfunction range

23 generic Sildenafil products — same molecule, different brands, formats and pack sizes.

How it works

Sildenafil works by blocking the PDE5 enzyme, which allows levels of a substance called cyclic guanosine monophosphate (cGMP) to rise in the tissues of the penis. This helps relax the blood vessels and improve blood flow when a man is sexually stimulated. Sexual arousal is still needed for the medicine to take effect; it does not cause an erection on its own. It generally begins to work within roughly half an hour to an hour and its effect usually lasts for a few hours.

How it is taken

Sildenafil is normally taken by mouth a short time before planned sexual activity, at the dose advised by your doctor. It can be taken with or without food, although a heavy or high-fat meal may delay how quickly it starts to work. As a general rule no more than one dose should be taken in any 24-hour period. Always follow the instructions in the patient information leaflet and the advice of your doctor or pharmacist.

Side effects

Common (usually mild and temporary):

  • Headache
  • Flushing of the face
  • Indigestion or stomach upset
  • Nasal congestion (blocked or runny nose)
  • Dizziness
  • Changes in vision such as a blue tinge or blurring

Stop and seek medical help if you experience:

  • A painful erection lasting longer than 4 hours (priapism) — seek urgent medical help
  • Sudden loss or decrease in vision in one or both eyes
  • Sudden loss or reduction in hearing, sometimes with ringing in the ears
  • Chest pain during or after sexual activity
  • Signs of a serious allergic reaction such as swelling of the face, lips or throat, rash or difficulty breathing

Safety & who should not take it

  • Must NOT be taken with nitrate medicines (used for chest pain/angina) or nitric-oxide donors such as amyl nitrite 'poppers', as this can cause a dangerous drop in blood pressure.
  • Use with caution if you have heart or blood-vessel disease, or if sexual activity has been advised against for heart reasons.
  • Tell your doctor about any liver or kidney problems, as a dose adjustment may be needed.
  • Caution is needed if you have low blood pressure or take alpha-blockers or other blood-pressure-lowering medicines.
  • Drinking alcohol can lower blood pressure further and may reduce the medicine's effectiveness.
  • Grapefruit and grapefruit juice may affect how the medicine works and are best avoided.
  • Not intended for use by women, children or anyone under 18 years of age.

Storage

Store in the original packaging below 30°C, out of the sight and reach of children, and do not use after the expiry date.

Frequently asked questions

How long does sildenafil take to work?+

It typically begins to work within around 30 to 60 minutes of being taken, though this can vary between individuals and may be delayed by a heavy meal. Check the patient information leaflet for guidance.

Can I take it with food?+

It can be taken with or without food, but a large or high-fat meal may delay the onset of its effect. Your doctor or pharmacist can advise on timing.

How is sildenafil different from Viagra?+

Sildenafil is the active ingredient and the generic equivalent of the branded medicine Viagra; both contain the same active substance and work in the same way.

Important: This information is general and not a substitute for medical advice. Always read the patient information leaflet supplied with your medicine and consult a doctor or pharmacist before use — especially if you have existing health conditions or take other medication.

Sildenafil health guides

Generic Sildenafil: The Complete Buyer's Guide

Summary: Generic sildenafil contains the same active ingredient as the original branded medicine and, when sourced from GMP-certified manufacturers, offers comparable quality at a lower cost. This guide explains how sildenafil works, what strengths and formats are available, the key safety point about never combining PDE5 inhibitors with nitrates, and how to verify a genuine product through batch numbers, manufacturer transparency, and proper packaging — while leaving the actual dose decision to your doctor or pharmacist.

Read guide

Cheap Generic Viagra: Getting Real Value Safely

Summary: Cheap generic Viagra simply means sildenafil citrate sold under its chemical name rather than a branded product, with the same active ingredient and manufacturing standards. Genuine value comes from comparing cost per tablet across pack sizes rather than chasing the lowest headline price, while keeping safety checks — the patient leaflet, nitrate interactions, and a pharmacist's advice — as the starting point every time.

Read guide

Is There a 'Better' Viagra? Comparing Your Options

Summary: There's no single "better" PDE5 inhibitor — sildenafil, tadalafil, vardenafil and avanafil all work the same way but differ in onset, duration and sensitivity to food, so the right choice depends on your routine and how your body responds. Sildenafil and vardenafil act faster with a shorter window and are more affected by meals, while tadalafil lasts far longer and avanafil can act quickly with a moderate duration. Whichever you're considering, PDE5 inhibitors must never be combined with nitrates, and the final decision should always involve the patient leaflet and a doctor or pharmacist.

Read guide

Erectile Products for Men: A Complete Overview

Summary: Erectile dysfunction treatments share the same core active ingredients — PDE5 inhibitors like sildenafil and tadalafil — but come in several formats including standard tablets, oral jelly, effervescent tablets, chewables, and combination tablets, each suited to different preferences around swallowing, discretion, or routine. Choosing a format is mostly about personal convenience, while strength, frequency, and suitability should always be confirmed with a doctor or pharmacist and the patient information leaflet.

Read guide

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